Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

Jonathan C. Barnes, Albert C. Fahrenbach, Scott M. Dyar, Marco Frasconi, Marc A. Giesener, Zhixue Zhu, Zhichang Liu, Karel J. Hartlieb, Ranaan Carmieli, Michael R Wasielewski, J. Fraser Stoddart

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Abstract

The kinetics and thermodynamics of intramolecular electron transfer (IET) can be subjected to redox control in a bistable [2]rotaxane comprised of a dumbbell component containing an electron-rich 1,5-dioxynaphthalene (DNP) unit and an electron-poor phenylenebridged bipyridinium (P-BIPY2+) unit and a cyclobis (paraquatp-phenylene) (CBPQT4+) ring component. The [2]rotaxane exists in the ground-state co-conformation (GSCC) wherein the CBPQT4+ring encircles the DNP unit. Reduction of the CBPQT 4+ leads to the CBPQT2(•+) diradical dication while the P-BIPY2+ unit is reduced to its P-BIPY•+ radical cation. A radical-state co-conformation (RSCC) results from movement of the CBPQT2(•+) ring along the dumbbell to surround the P-BIPY •+ unit. This shuttling event induces IET to occur between the pyridinium redox centers of the P-BIPY•+ unit, a property which is absent between these redox centers in the free dumbbell and in the 1:1 complex formed between the CBPQT2(•+)ring and the radical cation of methyl-phenylene-viologen (MPV•+). Using electron paramagnetic resonance (EPR) spectroscopy, the process of IET was investigated by monitoring the line broadening at varying temperatures and determining the rate constant (kET =1.33 × 107 s-1) and activation energy (ΔG = 1.01 kcal mol-1) for electron transfer. These values were compared to the corresponding values predicted, using the optical absorption spectra and Marcus-Hush theory.

Original languageEnglish
Pages (from-to)11546-11551
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume109
Issue number29
DOIs
Publication statusPublished - Jul 17 2012

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Electrons
Rotaxanes
Oxidation-Reduction
Cations
Paraquat
Electron Spin Resonance Spectroscopy
Thermodynamics
Spectrum Analysis
Temperature

ASJC Scopus subject areas

  • General

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Barnes, J. C., Fahrenbach, A. C., Dyar, S. M., Frasconi, M., Giesener, M. A., Zhu, Z., ... Stoddart, J. F. (2012). Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle. Proceedings of the National Academy of Sciences of the United States of America, 109(29), 11546-11551. https://doi.org/10.1073/pnas.1201561109

Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle. / Barnes, Jonathan C.; Fahrenbach, Albert C.; Dyar, Scott M.; Frasconi, Marco; Giesener, Marc A.; Zhu, Zhixue; Liu, Zhichang; Hartlieb, Karel J.; Carmieli, Ranaan; Wasielewski, Michael R; Stoddart, J. Fraser.

In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 109, No. 29, 17.07.2012, p. 11546-11551.

Research output: Contribution to journalArticle

Barnes, JC, Fahrenbach, AC, Dyar, SM, Frasconi, M, Giesener, MA, Zhu, Z, Liu, Z, Hartlieb, KJ, Carmieli, R, Wasielewski, MR & Stoddart, JF 2012, 'Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle', Proceedings of the National Academy of Sciences of the United States of America, vol. 109, no. 29, pp. 11546-11551. https://doi.org/10.1073/pnas.1201561109
Barnes, Jonathan C. ; Fahrenbach, Albert C. ; Dyar, Scott M. ; Frasconi, Marco ; Giesener, Marc A. ; Zhu, Zhixue ; Liu, Zhichang ; Hartlieb, Karel J. ; Carmieli, Ranaan ; Wasielewski, Michael R ; Stoddart, J. Fraser. / Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle. In: Proceedings of the National Academy of Sciences of the United States of America. 2012 ; Vol. 109, No. 29. pp. 11546-11551.
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abstract = "The kinetics and thermodynamics of intramolecular electron transfer (IET) can be subjected to redox control in a bistable [2]rotaxane comprised of a dumbbell component containing an electron-rich 1,5-dioxynaphthalene (DNP) unit and an electron-poor phenylenebridged bipyridinium (P-BIPY2+) unit and a cyclobis (paraquatp-phenylene) (CBPQT4+) ring component. The [2]rotaxane exists in the ground-state co-conformation (GSCC) wherein the CBPQT4+ring encircles the DNP unit. Reduction of the CBPQT 4+ leads to the CBPQT2(•+) diradical dication while the P-BIPY2+ unit is reduced to its P-BIPY•+ radical cation. A radical-state co-conformation (RSCC) results from movement of the CBPQT2(•+) ring along the dumbbell to surround the P-BIPY •+ unit. This shuttling event induces IET to occur between the pyridinium redox centers of the P-BIPY•+ unit, a property which is absent between these redox centers in the free dumbbell and in the 1:1 complex formed between the CBPQT2(•+)ring and the radical cation of methyl-phenylene-viologen (MPV•+). Using electron paramagnetic resonance (EPR) spectroscopy, the process of IET was investigated by monitoring the line broadening at varying temperatures and determining the rate constant (kET =1.33 × 107 s-1) and activation energy (ΔG‡ = 1.01 kcal mol-1) for electron transfer. These values were compared to the corresponding values predicted, using the optical absorption spectra and Marcus-Hush theory.",
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